Isomerization of olefins



Patented Get. 16, 1945 ,ttt,ttt

ISOMERIZATION OF OLEFINS Paul L. Cramer', Highland Park, Mich., assignorto General Motors Corporation, Detroit, Mich'., a corporation ofDelaware I No Drawing. Application July 28, 1943,

Serial No. 496,474

6 Claims.

This invention relates generally to the isomerization of olefins andmore particularly to the isomerization of branched-chain olefins.

The isomerization of olefins has been heretofore carried out by means ofa variety of catalysts. The most effective catalysts, such as sulphuricacid, phosphoric acid, or certain salts of these acids, give in mostinstances undesirable side reaction products. These side reactionproducts, polymers or oxidized material, cause a marked decrease in theactivity of the catalyst.

I have discovered that concentrated aqueous hydrochloric acid may act asa true catalyst for the isomerization of certain olefins. This isbrought about by heating small amounts of the concentrated acid with theolefin for comparatively long contact times. The reaction includes onlybranched-chain olefins having the double bond adjacent to the branch andinvolves a shift in the double bond as may be illustrated by thefollowing typical reaction:

The above equilibrium is determined by reaction temperature and may beapproached from either side.

The reaction is preferably carried out in the liquid phase at reactiontemperatures on the order of 100 to 200 C. or somewhat highertemperature by either static or flow methods. The reaction pressure isdetermined by the vapor pressure of the olefin at any particulartemperature.

' Concentrated aqueous HC1 containing 20% to 37% HC1 may-be used, thehigher concentration of acid being preferred. The molar concentrationsof the reactants may vary considerably. For example the following limitsmay be used:

zeo-csaz) Olefin, 93 mole percent Acid on basis of HC1, '7 mole percentOlefin, mole percent ,Acid on basis of HC1 20 mole percent Higher molarconcentrations of the acid increase the reaction rate but give greatlyincreased amounts of alkyl chlorides as side reaction products. At lowermolar concentrations of acid, much longer contact times are required toreach equilibrium for the isomerization reaction. The preferred molarconcentrations are olefin 89% and HC1 11%.

The following may be given as typical examples of specific procedure:

Example 1 2,3-climethylbutene-1 and concentrated hydrochloric acid (37%)in the volume ratio of parts of olefin to 8.5 parts acid were heated ina closed glass container for three hours. After cooling the reactionmixture, the aqueous acid layer was separated and the reaction productsWashed and dried. As analyzed by fractionation, 75% of.

the 2,3-dimethylbutene-1 was isomerized to 2,3- dimethylbutene-Z. About2% of 2-chloro2,3-dimethylbutene was formed as a side reaction product.

Example 2 The following table summarizes certain results obtained inisomerizing 2,3-dimethylbutene-1 to 2,3-dimethylbutene-2 by use ofaqueous hydrochloric acid as a catalyst. In this reaction the branchwhich includes mixing the branched-chain olefin with concentratedaqueous hydrochloric acid having a concentration ranging from 20% to37%, said branched-chain olefin being 80 to 93 preferred reactiontemperature and time are 150 mole per cent and the hydrochloric acidbeing C. and 3 hours respectively:

from '7 to mole per cent of the mixture, and

Isomerization of 2,3-dz'methylbutene-1 to 2,3-dimethyZbutene-2 by. theuse of aqueous hydrochloric acid as a catalyst 2 3d th I Aqueous H01 ggggigfgg R 1; Reaction products I ime y esc ion somerizabl ltGDG-l, partstenp, {$322.2 tion, perby volume Parts by P 01 fi Hm fiklllrgl Olefincent volume cent 9 n fii percent 61. 5 5 37 90 10 150 3 2 98 70 100 5 3793 7 150 3 1 99 23 100 8. 5 37 89 11 150 3 2 98 75 61. 5 1 37 9S 2 150 3Trace 10() 10 160 18 2O 89 11 150 3 2 9B 55 100 8. 5 3T 89 11 5O 1 2 Q817 100 8. 5 37 89 11 100 3 2 98 65 100 8. 5 37 89 11 200 2 2 Q8 65 61. 55 37 90 10 150 2 2 98 45 Other branched-chain olefins having the doublebond adjacent the branch may be treated in a manner similar to that ofthe procedure in the examples above.

.Various changes and modifications may be made without departing fromthe principles of my invention and I do not intend to limit the patentgranted for my invention.

I claim:

1. A process of isomerizing a branched-chain olefin having the doublebond adjacent to the branch which includes providing a mixture of thebranched-chain olefin and concentrated aqueous heating the mixture ofthe branched-chain olefin and the acid at a temperature on the order of100 to 200 C. for a time between one and three hours.

3. A process as in claim 2 in which the branched-chain olefin is2,3-dimethylbutene-L 4. A process as in claim 2 in which thebranched-chain olefin is 2-methylbutene-l.

5. A process of isomerizing 2,3-dimethylbutene- 1 to2,3-dir'nethylbutene-2 which includes providing a mixture of2,3-dimethylbutenel and concentrated aqueous hydrochloric acid having aconcentration of 37% in the volume ratio of 100 to 8.5, and heating saidmixture at a temperature of C. for about three hours.

6. A process of isomerizing 2'-methylbutene-l to 2-methylbutene-2 whichincludes providing a mixture of Z-methylbutene-l and concentratedaqueous hydrochloric acid having a concentration of 37% in the volumeratio of 100 parts olefin to 8 parts acid, and heating the mixture at150 C. for about three hours.

PAUL L. CRAMER.

